Tellann was the Elder warren used by the Imass. Later, Imass bonecasters used the power of Tellann to invoke the first Ritual of Tellann and thereby creating the T'lan Imass and changing Tellann forever.
A remnant of Tellann from before the ritual was shown in the Refugium. Tellann was said to gift the world with fire and heat in a world of cold emptiness.
Beak observed that Stormy and Gesler were "reforged in the fires of Tellann". He then went on to say:" Telas, Kurald Liosan, the fires, the ones dragons fly through to gain immunities and other proofs against magic and worse".